(1) Field of the Invention
This invention is in the field of methods and apparatus for minimizing unpredictable sources of error voltages in packaged precision analog components.
(2) Description of the Prior Art
Designers of systems that require precision analog components are always seeking such components that are more accurate, i.e., components in which the error voltages, or noise, are minimized to the maximum extent possible without degrading the reliability or increasing the costs of such components. Examples of such precision analog components are bipolar and FET input operational amplifiers, instrument amplifiers, voltage references, preamplifiers, discrete components, and multifunction circuits.
The sources of noise, or error voltages, in such components can be divided into two categories, the predictable sources of error voltages and the so-called unpredictable sources. Predictable sources of error voltages can be compensated by improved design, precise trimming, and improved manufacturing techniques which include enclosing such components in hermetic packages.
The prior art has identified two of the unpredictable sources of noise as being caused by temperature gradients in the dice, or I.C. chips, of the component and by temperature differences between the junctions of the leads of a packaged component, one junction being internal, or within the package and the other junction being external, made with conductors on substrates, or printed circuit (P.C.) boards on which the package containing the component is mounted. One prior art solution to minimizing error voltages from the above-identified sources is to enclose the entire system of which the precision component or components are a part in a suitable enclosure which maintains all of the elements at a substantially constant temperature. A prior art solution to the thermal gradient problem is to provide the components with an on chip stabilizer circuit which maintains the temperature of the chips, or dice, substantially constant. However, in many applications the prior art solutions to the problem of minimizing error voltages in precision analog components is either not possible or is not economically feasible. The problem not solved by the prior art is how to minimize the so-called unpredicable sources of error in individually packaged precision analog components without requiring the entire system of which the component is a part to be provided with or packaged in an ideal environment; or, stated another way, to provide each packaged precision analog component with its own idealized environment.